As a countermeasure to ESD (Electro Static Discharge) in a semiconductor device, there has been known a technique where a Zener diode which protects a semiconductor element is incorporated into the semiconductor device. However, there exists a possibility that a large electric current flows into the Zener diode thus breaking the Zener diode. There also exists a possibility that some of the electric current is not absorbed by the Zener diode and flows into an element portion of the device, thus breaking the element by heat or overvoltage or overcurrent thereof. To avoid such a situation, there has been proposed a method where a P/N-junction area of the Zener diode is increased so that a dynamic resistance of the Zener diode is lowered.
However, in a situation where a size of a semiconductor device is miniaturized, when a P/N-junction area is simply increased, an element area is decreased thus giving rise to a drawback that the ON resistance of the semiconductor device is increased.